For the past decade or so, sports scientists have been obsessed with the benefits of heat training. The extra stress of heat triggers various adaptations that help you handle hot conditions, like more sweating. Some of these adaptations, like increased blood volume, may even give you a boost when competing in cooler conditions. As a result, many top athletes now incorporate elaborate heat protocols into their training.
What if the opposite is also true? At a conference in Montreal last month, a physiologist named Dominique Gagnon presented new data suggesting that cold training might offer some unique metabolic benefits that translate into enhanced health and endurance performance. It’s just a hypothesis at this point, based on a decade’s worth of incremental research. But as we head into the darkest, coldest months of the year, it’s kind of nice to think that our winter training might pack an extra punch.
Gagnon is a Canadian who recently moved from Laurentian University, in northern Ontario, to Finland’s University of Jyväskylä, three hours north of Helsinki. He knows cold, in other words. At the annual Canadian Society for Exercise Physiology conference, he presented preliminary data comparing the training effects of working out in either warm (77 degrees Fahrenheit) or cool (32 degrees) conditions. The goal was to figure out whether training in the cold would boost mitochondria levels, which is one of the key adaptations that underlies aerobic fitness.
What’s So Great About Cold?
Gagnon’s research on exercise in the cold goes back over a decade. Back in 2013, for example, he published data showing that cold-weather exercise relies on a different fuel mix than warmer conditions, burning more fat and less carbohydrate. He suspects that this is because when you’re exercising in comfortable temperatures, there’s actually some local overheating in the muscles themselves.
Human metabolism is only about 25 percent efficient—comparable to the internal combustion engine in your car—so three-quarters of the energy in your food is released as heat in the muscles. That means that the temperature inside your muscles can be high even when the rest of you is cool. The advantage of exercising in the cold, then, is that it prevents your muscle cells from overheating and enables them to keep burning more fat for aerobic energy, which relies on the mitochondria in your muscles. In the long run, that should boost mitochondria levels and train your body to become more efficient aerobically.
There are various other hints supporting this view. Researchers at the University of Nebraska at Omaha, for example, found that exercise in the cold produced a bigger spike in the cellular signals that tell the body to produce more mitochondria, though the difference wasn’t statistically significant. And studies in mice have shown that they get a bigger fitness boost from exercise when the air is mildly cold.
The New Findings on Cold Training
In Gagnon’s new study, 34 volunteers trained three times a week for seven weeks, doing interval workouts on an exercise bike. Before and after the training period, they had muscle biopsies, which involve removing a small chunk of muscle from the leg, in order to analyse how much mitochondria was present. Sure enough, the group that trained in 32-degree air had a significantly greater increase in several different markers of mitochondrial content. Gagnon is still analyzing the VO2 max data, but initial signs are that those training in the cold were more likely to see a significant increase.
Those are encouraging findings. But even if the results (which have not yet been peer-reviewed) hold up, the next big question is whether this approach is practical. How cold do you have to be? Gagnon’s subjects performed their cold training in the equivalent of shorts and a T-shirt, which is less than I would typically wear at that temperature, but not totally unreasonable. Would the effects be nullified if you wore a long-sleeve shirt and tights? Gagnon’s not sure yet—but he emphasized that the goal isn’t to be cold, with measurably lower muscle and body temperature. Instead, it’s to avoid letting your muscles get too hot.
At this point, it’s worth flashing back to some findings I wrote about earlier this year. Stephen Cheung and his colleagues at Brock University in Canada showed that getting superficially cold, with no drop in core temperature, reduced time to exhaustion in a cycling test by about 30 percent. That involved sitting in a 32-degree room with a light breeze for half an hour before the subjects even started cycling. Staying in the room for longer, so that their core temperature actually dropped by a degree, reduced endurance by another 30 to 40 percent. This is not what Gagnon is aiming for.
Instead, the goal of cold training seems to be to let yourself get just cool enough that your muscles don’t overheat. Where that threshold is remains to be determined, and the results will need to be replicated before anyone takes them seriously. Gagnon is in discussions with the Finnish military, which has lots of personnel engaging in physical activity in perennially cold conditions, about further studies. Maybe it will turn out to be the next big thing in endurance training. Or maybe not. To be totally honest, I normally wouldn’t write about such preliminary results—but the idea that it might be true will help get me through some cold training runs this winter.
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